Drugs are available which enhance the activity of a hematopoietic (bloodforming) system. Such a system replenishes the multiplicity of blood cell types found in a healthy animal, including white blood cells (neutrophils, macrophages, and basophil/mast cells), clot forming cells (megakaryocytes, platelets), and red blood cells (erythrocytes).
The average human male's hematopoietic system has been estimated to produce on the order of 4.5.times.10.sup.11 granulocytes and erythrocytes every year, which is equivalent to an annual replacement of total body weight [Dexter et al., (1985) BioEssays, vol. 2:154-158]. Current scientific understanding proposes that small amounts of specific hematopoietic growth factors direct the proliferation, differentiation, and maturation of each of the various hematopoietic cell types from a small population of pluripotent hematopoietic stem cells. These various growth factors act at different times on different cell populations, ultimately giving rise to a functional hematopoietic system. Drugs such as erythropoietin enhance the production of erythrocytes, or red blood cells, which transport oxygen to the various tissues of the animal's body. The process of producing erythrocytes ("erythropoiesis") occurs continuously throughout an animal's life span to offset erythrocyte destruction. The typical red blood cell has a relatively short life-span, usually 100 to 120 days; Gray's Anatomy, Williams et al. eds., Churchill Livingstone, 1989, p. 665. Erythropoiesis is a precisely controlled physiological mechanism whereby sufficient numbers of erythrocytes are produced to enable proper tissue oxygenation, but not so many as to impede circulation.
Erythropoietin (EPO) is a hormone or more specifically a peptide hormone largely produced in the peritubular interstitial cells of the kidneys. EPO is produced as the result of the expression of a single copy gene. A DNA molecule encoding a DNA sequence for human EPO has been isolated and is described in U.S. Pat. No. 4,703,008, hereby incorporated by reference, and hereinafter referred to as the '008 patent." Also, DNA molecules coding for EPO from monkeys [Lin et al., (1986) Gene, vol. 44, pp: 201-209] and mice [McDonald et al., (1986) Mol. Cell Biol., pp: 842] have been described. The amino acid sequence for recombinant human EPO ("rHuEPO") is identical to the sequence for EPO obtained from human urinary sources. However, as could be expected, the glycosylation of rHuEPO differs from that of urinary EPO and human serum EPO. See, e.g. Starring et al. (1992), J. Endocrin., vol. 134, pp: 459-484; Strickland et al. (1992), J. Cell. Biochem., suppl. 16D, p. 324; Wide et al. (1990), Br. J. Haematol., vol. 76, 121-127.
EPO is normally present in the blood plasma in very low concentrations, as the tissues are being sufficiently oxygenated by the existing number of circulating erythrocytes. The EPO present stimulates the production of new erythrocytes to replace those lost to the aging process. Additionally, EPO production is stimulated under conditions of hypoxia, wherein the oxygen supply to the body's tissues is reduced below normal physiological levels despite adequate perfusion of the tissue by blood. Hypoxia may be caused by hemorrhaging, radiation-induced erythrocyte destruction, various anemias, high altitude, or long periods of unconsciousness. In contrast, should the number of red blood cells in circulation exceed what is needed for normal tissue oxygenation. EPO production is reduced.
Recombinant human EPO (rHuEPO) is being used therapeutically in a number of countries. In the United States, the U.S. Food and Drug Administration (FDA) has approved rHuEPO's use in treating anemia associated with end-stage renal disease. Patients undergoing hemodialysis to treat this disorder typically suffer severe anemia, caused by the rupture and premature death of erythrocytes as a result of the dialysis treatment. EPO is also useful in the treatment of other types of anemia. For instance, chemotherapy-induced anemia, anemia associated with myelodysplasia, those associated with various congenital disorders, AIDS-related anemia, and prematurity-associated anemia, may be treated with EPO. Additionally, EPO may play a role in other areas, such as helping to more quickly restore a normal hematocrit in bone marrow transplantation patients, in patients preparing for autologous blood transfusions, and in patients suffering from iron overload disorders. See e.g. U.S. Pat. No. 5,013,718, hereby incorporated by reference.
The effective use of EPO as a therapeutic agent requires that patients be administered small but highly precise doses of the protein in stable, pharmaceutically acceptable formulations. For an example of a current EPO formulation, see Sobata, J., Erythropoietin in Clinical Applications, Garnick, M., ed. Marcel Dekker, Inc., New York (1990). Current therapy for end-stage renal disease calls for intravenous EPO administration within twelve hours of dialysis, three times a week. Alternatively, EPO may be administered to such patients by intravenous, intramuscular, intracutaneous, or subcutaneous injection. U.S. Pat. No. 5,354,934 (incorporated herein by reference) shows that a nebulizer can deliver EPO to the circulatory system of a rat.
The instant invention is based upon the unexpected discovery that EPO may be efficiently and accurately administered by inhalation in a therapeutically efficacious manner by a small self-contained hand-held device. EPO delivered to the lung in this manner is absorbed into the patient's bloodstream for systemic distribution. This new route of EPO administration enables the rapid delivery of a specified medicament dosage to a patient without the necessity for injection. In addition, pulmonary administration more readily lends itself to self-administration by the patient.
There has been some prior success in the pulmonary administration of pharmaceutical compositions comprised of hormones. Hormones such as EPO are currently administered by injection. Because the stomach presents a highly acidic environment, oral preparations of peptides are unstable and readily hydrolyzed in the gastric environment. Currently, there are no oral preparations of EPO or any other therapeutic peptide agents available.
Both calcitonin and leuprolide can be administered nasally. (See Rizzato et al., Curr. Ther. Res. 45:761-766, 1989.) Both drugs achieve blood levels when introduced into the nose from an aerosol spray device. However, experiments by Adjei et al. have shown that the bioavailability of leuprolide when administered intranasally is relatively low. Adjei and Garren, Pharmaceutical Research, Vol. 7, No. 6, 1990.
An increase in the bioavailability of leuprolide can be obtained by administering the drug into the lung. Intrapulmonary administration of leuprolide has been shown to be an effective means of non-invasive administration of this drug. Adjei and Garren, Pharmaceutical Research, Vol. 7, No. 6, 1990. Intrapulmonary administration of leuprolide and other peptide drugs has the additional advantage of utilizing the large surface area available for drug absorption presented by lung tissue. This large surface area means that a relatively small amount of drug comes into contact with each square centimeter of lung parenchyma. This fact reduces the potential for tissue irritation by the drug and drug formulation. Adjei et al., demonstrated that peptide drugs could be successfully delivered to a patient by the intrapulmonary route without the need for any permeation enhancers. Local irritation has been seen with nasal delivery of insulin and has been a problem for commercialization of nasal preparations of that drug.
Hormones such as leuprolide and EPO are very potent with effects that are not immediately manifested. For example, therapy with leuprolide for prostrate cancer does not typically produce any acute clinical effects. Similarly, prophylaxis against osteoporosis with calcitonin will not produce any acute symptoms discernible to the patient. Therefore, administration of each dose of these drugs must be reliable and reproducible. Careful compliance monitoring is important to avoid therapeutic failures by carefully following the patient's adherence to the prescribed dosing regiment. In addition, because these drugs are potent therapeutic agents, care must be taken to avoid overdosing.
Pulmonary administration of .alpha.-1-proteinase inhibitor to dogs and sheep has been found to result in passage of some of that substance into the bloodstream. See Smith et al., J. Clin. Invest., vol. 84, pp. 1145-1154 (1989). Likewise, aerosolized .alpha.-1 anti-trypsin diffused across the lung epithelium and entered into systemic circulation in sheep and humans. See Hubbard et al., (1989) Ann. Intern. Med., vol. 111, pp. 206-212.
Experiments with test animals have shown that recombinant human growth hormone, when delivered by aerosol, is rapidly absorbed from the lung and produces faster growth comparable to that seen with subcutaneous injection. See Oswein et al., "Aerosolization of Proteins", Proceedings of Symposium on Respiratory Drug Delivery II, Keystone, Colo., March, 1990. Recombinant versions of the cytokines gamma interferon (IFN-.gamma.) and tumor necrosis factor alpha (TNF-.alpha.) have also been observed in the bloodstream after aerosol administration to the lung. See Debs et al., The Journal of Immunology, Vol. 140, pp. 3482-2388 (1988). Likewise, Pitt et al. have recently demonstrated the feasibility of pulmonary delivery of granulocyte-colony stimulating factor (G-CSF) to mammals. See published PCT application WO94/20069 published Sep. 15, 1994 and incorporated herein by reference.
The lungs contain 3.times.10.sup.8 alveoli with a total surface area of approximately 140 m.sup.2. Alveoli are thin walled pouches that represent as minimal a barrier to gaseous exchange between the atmosphere and blood as is possible without comprising the integrity of the lung. Correspondingly, capillary beds adjacent to the alveoli are estimated to share a surface area of 125 m.sup.2 with the alveoli [Gray's Anatomy, supra]. Thus, each alveolus is in intimate association with numerous blood-bearing capillaries bringing oxygen-depleted blood from distal body tissues.
Based on the above cited publications it can be seen that the pulmonary delivery of many types of peptide drugs is known. By administering large amounts of an aerosolized drug containing formulation a therapeutic level of the drug in the circulatory system can be obtained. For example, a nebulizer can be used and the subject can breath aerosolized formulation from the nebulizer for a long enough period to obtain a therapeutically effective level. However, such a procedure is not only inefficient it does not allow for precise dosing.
The most convenient form for intrapulmonary administration of drugs by ambulatory patients is through the use of a metered dose inhaler. Metered dose inhaler devices allow the self-administration of a metered bolus of drug when the device is manually actuated by the patient during inspiration. However, such devices must be used with the proper inspiratory maneuver in order to promote effective deposition of the drug into the lung. In addition to performing a correct inspiratory maneuver, the patient must self-actuate the metered dose inhaler during the appropriate part of the inspiratory cycle. Further, when using such devices, it is not typically self-evident to the patient that the drug was properly or improperly administered. For those drugs without immediate clinical effect, the patient can easily misuse the metered dose inhaler and be under the false impression that he is correctly self-administering the drug as prescribed. Similarly, the patient may be under the false impression that he performed an incorrect inspiratory maneuver in metered dose inhaler actuation when he in fact properly performed these operations and received an appropriate amount of drug.
Devices exist to deliver metered dose inhaler drugs into the lung in a breath-actuated manner. However, such devices do not measure inspiratory flow rate and determine inspiratory volume in order to trigger the device. Therefore, a sub-optimal inspiratory maneuver (e.g. one with too high of an inspiratory rate) could be used to actuate the device and produce a sub-optimal deposition pattern of drug into the lungs resulting in a sub-therapeutic blood level of the therapeutic agent being delivered. If delivery took place at the correct point in the inspiratory cycle the dose delivered would be high--overall dosing would be erratic in that drug is released at different points in the inspiratory cycle.
When using a metered dose inhaler, the dosing events must be manually recorded by the patient. Many potent therapeutic hormone peptide drugs are given only once a day. It is important that the patient remember to take the prescribed daily dose, and that the dose be taken at the correct time of the day. Further, it is important that the patient not take more than the prescribed number of doses per day. The timing of delivery of potent therapeutic hormone peptide drugs is critical because these drugs interact intimately with the chronobiology of the patient's physiology in order to produce their desired effect.
When using standard metered dose inhaler devices, the patient must manually record the time of each dosing administration. In addition, the patient must remember when to self-administer the drug. Devices exist for recording automatically metered dose inhaler drug delivery events. However, such devices do not record the presence of inspiratory flow at the time of device firing. This means that a noncompliant patient can fire the metered dose inhaler into the air and have a valid drug dosing event recorded on the self-containing recording means. In addition, the patient could self-administer the drug with an inappropriate inspiratory maneuver and have a valid drug dosing event recorded by the device. This would lead the physician to assume that the patient was compliant when he was receiving an inappropriate amount of drug with each dosing event.
The present invention endeavors to provide an efficient method for the pulmonary delivery of EPO to a patient in a manner such that dosing is closely controlled and administration is from a convenient, hand-held device.